1. Field of the Invention
The invention relates to copolymers of monoethylenically unsaturated acid-group-containing monomers and a further hydrophobic monomer component for prevention of inorganic and organic deposits in water-conveying systems, as well as to a method for synthesis of same.
2. Description of the Background
Water-conveying systems such as water and wastewater piping systems, cooling or heating loops, cooling lubricant systems, drilling fluids or production process water for material transport contain a large number of microorganisms, such as bacteria of the species Pseudomonas vesicularis, Enterobacter cloacae, citrobacter freundii and Enterobacter amnigenus, which because of the conditions to be encountered in these systems exhibit rapid growth. The proliferation and metabolism of the microorganisms can therefore lead to formation in these media of biological masses known as extracellular polymer substances, which often form gels together with inorganic polyvalent cations and adhere to equipment parts.
The deposits can lead in piping systems to a considerable pressure loss, which is disproportionately large compared with the resulting cross-sectional narrowing. Furthermore, these deposits can accelerate the corrosion of equipment parts, since the concentration of oxygen, the redox potential, the salt content and thus the conductivity are locally different from those in the other surroundings. If larger structures form from such deposits, the danger exists that they will be detached and leads to problems in machinery and production masses.
In cooling loops, the deposits represent an insulating layer, which can greatly reduce heat-transfer efficiency, since heat transfer takes place by diffusion rather than by convection at the locations of the deposits. It must be pointed out that organic coatings produce a much greater insulating effect than inorganic coatings.
Of particular importance are mixtures of organic and inorganic coatings, since organic coatings find favorable growth and viability conditions in the surface-rich inorganic coatings.
Especially in paper manufacture, these biological growth processes must be prevented in the production process. At present, microbicides (biocides, slimicides) based on intensively acting, toxic substances are used for this purpose.
Besides the problems associated with safe handling and transportation of such toxic substances, and that of limiting the effect to the desired area of application, it is necessary to use several of these microbicides in combination and in an alternating sequence, in order to counter the resistance of the microorganisms to the very product being used. In addition, the killing of microorganisms does not simultaneously mean that they have been removed from the system. In many cases, dead biomass remains behind, forming a source of nutrition for subsequent microorganisms. The deposits are simultaneously a barrier against biocides, and can effectively prevent them from penetrating. Thus it is critical to remove such gels and deposits from the system.
In WO 95/15296 there are described oil-in-water emulsions that prevent slime formation in water-conveying systems. The described oil-in-water emulsions are composed of a hydrophobic phase (oil phase), at least one emulsifier and water, and their hydrophobic phase contains an active agent that may be an acyclic, monocyclic and/or bicyclic terpene, especially a terpene hydrocarbon. Disadvantages are that only organic coatings can be prevented and that an emulsion is involved. It is known to the person skilled in the art that, depending on handling, storage temperature and storage time, emulsions tend to separate, thus losing their effect.
Besides the organic deposits due to microbial processes, deposits composed of resins and glue residues are present in the water-conveying systems of paper manufacture, especially in the processing of waste paper and recycled paper. These deposits can be formed even if the system does not contain any microorganisms. The negative effects on equipment parts and on the overall process are analogous to those described in the foregoing.
In U.S. Pat. No. 5,863,385 there is described the use of oil-in-water emulsions analogous to those of WO 95/15296 for the treatment of machinery in pulp, paper and cardboard manufacture and for cleaning such equipment of adhering contaminants in the form of natural resins and/or synthetic polymers, as well as for prevention of contamination of the equipment by such contaminants.
U.S. Pat. No. 5,916,857 describes the removal of sticky resin residues on paper machinery by cleaning agents composed of a mixture of aliphatic petroleum distillates, d-limonene and aliphatic dicarboxylic acid esters.
Besides the deposits of organic origin and composition just described, inorganic deposits formed from salts and compounds of the water used for the operating processes can occur in water-conveying systems. In particular, chlorides, sulfates, phosphates and hydrogen carbonates of the alkaline earths can be mentioned in this regard. Some of these cations and anions can form insoluble salts or oxides/hydroxides, which precipitate out if the respective solubility product is exceeded. The soluble hydrogen carbonates in particular are converted by heat to carbonates, and so part of the calcium salts precipitates out as poorly soluble calcium carbonate at high temperature. At high magnesium concentrations, magnesium carbonates can also precipitate out, as can even hydroxides at certain pH levels. A known coating problem in wastewater plants is also the formation of magnesium ammonium phosphate. Further possible deposits consist of calcium sulfate, silicates and phosphates in the most diverse forms, which tend to form coatings depending on system conditions, such as pH, temperature and degree of oversaturation.
In the area of paper manufacture, coatings of calcium oxalate are a particular problem, since oxalic acid occurs in wood and is formed during the bleaching process by oxidative decomposition of lignin and of monosaccharides, oligosaccharides or polysaccharides, such as xylane.
Substances that prevent the precipitation of poorly soluble compounds have long been known to the person skilled in the art as hardness stabilizers. Examples include inorganic polyphosphates, lignin sulfonates, naphthalenesulfonic acid condensation products, phosphonic acids, aminomethylene phosphonic acids, phosphoric acid esters, phosphonocarboxylic acids as well as polycarboxylic acids, as typified, for example, by partly saponified polyacrylamides or by polymers or copolymers of acrylic acid. A disadvantage of the cited substances is that some of these complexing agents are toxic and only inorganic deposits can be prevented.
Besides coatings of insoluble inorganic compounds that have just been formed, insoluble particles already present in the cooling system can also lead to coatings. This second large group of organic coating-forming substances is suspended solids, which result from the system or are introduced into the system from the air in the case of open cooling systems. The suspended solids sediment at places with very low flow velocities in the system. The coating formed in this way can also result from corrosion products of the materials, washed-in dust and solids from the make-up water. Furthermore, mixed deposits composed of sediments and hardness precipitates can also be formed.
Products that assume the function of dispersing agents, or in other words agents that stabilize solid particles against sedimentation and sludge formation by microdisperse distribution, have long been known, mostly from the polymer group. As an example, polycarboxylic acids of the type of partly saponified polyacrylamides are used for this purpose, as are polymers and copolymers of acrylic acid with various comonomers, as well as polystyrenesulfonates, polyvinylsulfonates, quaternary ammonium compounds of unsaponified polyacrylamides and polyalkylene glycols. The prior art is disclosed, for example, in the following publications: EP 818423 A1, U.S. Pat. No. 4,455,235, GB 2105319, GB 2152919. A disadvantage is that only inorganic deposits can be effectively prevented.
The person skilled in the art is aware that the chemical nature of the deposits in water-conveying systems is often not exactly known and that it fluctuates due to seasonal climatic variations. Because of the temperature-induced concentration fluctuations of dissolved gases, the content of soluble hardness builders varies simultaneously. The concentration of microorganisms is also subject to climate-related seasonal fluctuations. Thus, in a given production plant, it may be that different deposits must be prevented depending on the season, meaning in turn that different measures must be employed. This is particularly critical in periods when the weather is changing from winter to summer and vice versa.
Thus there has been no lack of attempts to suppress deposits simultaneously by the use of polymers and biocides, as described in EP 892838 B1 or WO 96/14092. A disadvantage in these methods also is the handling of toxic or hazardous biocides.
In U.S. Pat. No. 5,756,624 there are described terpene terpolymers composed of at least 10% terpene and of further monomers from the group of olefinically unsaturated monocarboxylic acids with 3 to 5 carbon atoms and their esters, obtained by the bulk polymerization method. One disadvantage among others in the described polymerization without solvents is that high temperatures are reached, causing undesired discoloration of the product. Furthermore, the polymers obtained are not water-soluble but at best are dispersible. It is proposed that they be used, among other purposes, as tackifying agents for adhesives and as builders.
The same is also true for DE 4332806 A1, in which the aforesaid uses are also described. This publication describes copolymers of terpenes without conjugated double bonds and vinyl compounds and/or dicarboxylic acids with a C—C double bond as well as their derivatives as comonomers, which preferably are obtained by means of radical bulk polymerization. Although organic liquids that have the ability to dissolve the terpene copolymers or the comonomers or monomers at room temperature are cited as organic solvents, this publication relies completely on radical bulk polymerization as the method for synthesis of the terpene copolymers described therein. A method for synthesizing these terpene copolymers by means of radical solution polymerization in the aqueous phase is not described. To the contrary, cationic and also radical solution polymerization processes are generally depicted as disadvantageous.
Copolymer dispersions that are dispersible only in water and that contain terpenes that are not soluble in water are described in DE 3536931 A1. The most important property of these copolymers cited therein is their suitability for use in binder dispersions, especially for industrial coatings, in which slight water uptake or water-induced swelling occurs and frequent or prolonged exposure of the coatings to water can be expected. Because of the aforesaid properties profile of these copolymers, it is not possible to use such copolymer dispersions containing these terpenes for prevention of inorganic and organic deposits in water-conveying systems, such as in service water or wastewater systems, in cooling loops, in seawater desalination plants, in reverse osmosis systems, or for conditioning of brackish water, for recovery of sugar from sugar beet, etc.
Radical copolymerizations of terpenes with maleic anhydride have also been described in Eur. Polym. J., 24 (5), 453-6, 1988. These reactions are performed as solution polymerizations, for example in tetrahydrofuran benzene, in dioxane or in toluene. These solvents, which in some cases are toxic and carcinogenic, must then be disposed of at considerable expense. Bulk polymerization is not described.